Process for polymerizing chloroprene in the presence of sulphur dioxide and product thereof



. Patented Mar. 12945 STATES PATENT OFFYCE PROCESS FOR POLYMERIZINGCHLORO- PEENE IN THE PRESENCE OF SULPHUR DI- OXIDE AND PRODUCT THEREOFHoward Warner Starkweather, Westover Hills, Del., assignor to E. I. duPont de Nemours & Company, Wilmington, Del., a corporation of 4 5Delaware at Drawing. Application March 1, 1940,

j, v 1 Serial No. 321,667

17 Claims.

Carothers and Collins, in their U. S. Patent No.

1,950,432, disclose that, by polymerizing chloro- 2-butadiene-1,3 undervarious conditions, it is possible to obtain products having a varietyof degrees of solubility, plasticity, elasticity, and strength. Theystate that light and pressure and catalysts, such as oxygen andperoxides, in-

fluence the polymerization. Carothers, Collins and Kirby disclose, intheir U. S; Patent No. 1,950,438, that the character of the product maybe modified by carrying out the polymerizationin the presence ofinhibitors. Among the inhibitors they investigatedwere various organicsulphur compounds. U. S. Patent No. 1,967,860, also issued to Carothers,Collins-and Kirby, discloses that this polymerization may 'be carriedout in the presence of various solvents.

The emulsification of chloro-2-butadiene-L3 and its polymerization inthat state to obtain a synthetic latex is disclosed in Collins U. S.Patent No. 1,967,861. Ordinarily, the product obtained by coagulatingthis emulsion after polymerization to a synthetic latex, is an elastic,nonplastic, cured rubber, but, if the chloro-Z-butadime-1,3 contains 1'per cent of iodine, it polymerizes to a plastic product. Collins alsodiscloses that the addition of diluents or solvents,

before or after emulsiflcation, tends to impart a] greater degree ofsoftness and plasticity to the "final product. Dales and Downing, in U.S. Patent No. 2,138,226, have described an improved method of emulsionpolymerization involving the use of different emulsifying agents.

Williams, in his U. 8. Patent No. 1,950,436,discloses that plasticpolymers may be produced by partially polymerizing chloro 2 butadiene1,3

and then separating the unpolymerized material. He describes a methodwhich involves partially polymerizing chloro-z-butadiene-Lti without theuse of solvents, dispersing media, and the like.

" This method is hereinafter referred to as massive" polymerization. Bysuitable compounding curing, these plastic polymers can be con- (Cl.260-79) I verted into an extremely tough elastic product resemblingvulcanized rubber.

Cured natural rubber is considerably swollen and deteriorated when itcomes in contact with many organic solvents. Chloropreneand similarhalogen substituted dienes may be polymerized according to a numberv ofprocesses, already published or in copending patent applications, toyield plastic, rubber-like polymers which have certain importantadvantages over natural rubber, one of which is greaterresistance in thecured state to organic solvents, particularlyhydrocarbons. For certainpurposes, however, products of even greater resistance are desired.

vThis application is a continuation-impart of applicants copendingapplication, Serial No. '69,- -739, filed March 19, 1936.

It is an object or this invention to provide an improved methodforpreparing derivatives oi .20 compounds of the general formula inwhich X is halogen and R is hydrogen or av hydrocarbon radical. Afurther object is to provide an improved method for polymerizinghalogen-2-butadienes-L3. A more specific object is to provide a methodby which high yields of plastic polymer may be producedfrom chloro-2-.80' butadiene-1,3 in a single polymerization. A still further object isto produce, in a single poly merization, high yields of a plasticpolymer of chloro-2-butadiene-1,3 of good stability resemblingunvulcanized Hevea rubber in its physical properties and capable ofbeing shaped and cured to form a tough elastic mass resemblingvulcanized natural rubber. Another object is to produce a plasticpolymer which can be readily. converted into an odorless elasticsubstance. An-

other object is to produce polymeric materials which may be processedlike natural rubber and which will have, in the cured state, a very highdegree of resistance to the action of hydrocarbon solvents. Otherobjects will appear herein- 5 after.

The objects are accomplished by polymerizing compounds of the generalformula CH2=(,)C=GHI o i X in which X is halogen and R is hydrogen or ahydrocarbon radical, and especially chloro-Z-butadiene-l,3, in thepresence of sulphur dioxide. Under preferred conditions, thechloro-2-buta- $6 dime-1,3 is polymerized in an. emulsified form in thepresence of sulphur dioxide. The preferred dispersing medium is water.The invention is described in detail, hereinafter, with refbe obviousthat its equivalents may be similarly employed.

The essential feature of the invention is that sulphur dioxide bepresent as such during the polymerization. Although, as indicated above,

the best results are obtained when polymerization .erence'to the use ofsulphur dioxide, but it will halogen diene while it is in solutioneither in a solvent or diluent such as benzene or carbon tetrachlorideor in a polymerizable solvent such as methyl methacrylate. Theunemulsiiied polymerization may be carried out, for example, accordingto the procedure of U. S. Patent No. 1,950,436.

v Polymerization of compounds of the class described in the presence ofsulphur dioxide unexpectedly results in yields of plastic polymer inexcess of 50 per cent.

In addition to producing a high yield of plastic polymer, the additionof sulphur dioxide gives a polymer which, when cured, has an increasedresistance to the action of solvents. The already good solventresistance of chloroprene polymers is materially increased. Thisincrease in solvent resistance is proportional to the amount of Suiphurdioxide in chemical combination with the chloroprene over ranges morefully set forth below.

The class of halogen dienes to which this invention has been found to beapplicable are those which have the above general formula. Thedefinitely preferred member of this group is chloro-2-butadiene-1,3,which, as has been previously disclosed, possesses the ability topolymerlze to a rubber-like material which is similar to natural rubber.Although the other halogen dienes included in the class, which'have thufar been tested, do not all possess this property to the same degree aschloroprene, they do, nevertheless, polymerize to more or lessrubber-like materials and it has been found that, if theirpolymerization is carried out in the presence of sulphur dioxide, animproved yield of a more plastic polymer is obtained as contrasted withthe product obtained. from the same halogen diene in the absence ofsulphur dioxide. Thus, an increased yield of more plastic polymer can beobtained from bromo-2-butadiene-1,3 and also fromchloro-2-methyl-3-butadiene-l,3 when they are polymerized in thepresence of sulphur dioxide. Mixtures of two or more halogen butadienesmay also be polymerized by the method of this invention. Similarincrease in solvent resistance is obtained.

The sulphur dioxide maybe brought into contact with the halogen diene,whether in solution, emulsion, or the massive state, in any convenientmanner, such as by the direct addition of gaseous or liquid sulphurdioxide or by the addition of a solution of sulphur dioxide in water orin an emulsifying solution or by dissolving the sulphur inafter;

dioxide in the halogen diene. Also, if desired, instead of addingsulphur dioxide as such, a salt, such as sodium bisulphite, may beadded, which, upon the addition of acid, will generate sulphur dioxide.

A. number of embodiments of the-present process are described in theexamples appearing here- These examples are directed to polymerizationin aqueous emulsion, the preferred type, but it will be understood thatsimilar considerations'will apply, in general, to polymerization in themassive state, in solution, etc. Thus. the amount of sulphur dioxidepresent may vary with reference to the amount of halogen diene.Likewise, various temperatures and pressures may be used as well asvarious concentrations of halogen diene in the mass in which thepolymerization is taking place.

Attention, is called to the fact that, in these examples, as well asthroughout the specification and claims, wherever the terms parts isused, it is intended to. mean parts by weigh The examples, of course,are merely illustrative, and it is not applicant's intention to belimited to the specific conditions of operation or other details thereinset forth.

Example I Two hundred fifty parts of chloro-Z-butadiene- 1,3 werethoroughly emulsified in 850 parts of 2 per cent cetyl trimethylammonium bromide aqueous solution. One hundred fifty parts of 2 per centcetyl trimethyl ammonium bromide aqueous solution containing 10 parts ofsulphur dioxide were immediately'added to the emulsion. This emulsionwas maintained-at 20 C. for 4 hours. Two and five tenths (2.5) parts ofphenyl beta naphthylamine dissolved in 25 parts benzene and emulsifiedwith 25- parts of 2 per cent cetyl trimethyl ammonium bromide aqueoussolution were then added. The polymer was next coagulated by adding theemulsion to an equal volume of ethyl alcohol and separated from theserum. Volatile material was removed by working the coagulated polymerto constant weight on a rubber mill.

A 73.5 per cent yield of polymer with a plasticity number of 94 and goodaging properties was obtained by this method. (Plasticity number, asused herein, is the thickness in thousandths of an inch of a sample 2.5co. in volume in the form of a cylinder in diameter which has beenheated to C. for. 15 minutes and then kept under a weight of 5 kilogramsfor 3 minutes at 80 C.) One hundred parts of this polymer was compoundedwith 5 parts of zinc oxide, 10 parts of magnesium oxide, and 5 parts ofrosin and heated for 30 minutes at 142 C.- The resulting product had atensile strength of 3250 pounds per square inch.

(Nora: The addition of phenyl-beta-naphthylamine, coagulation with ethylalcohol, separation from the serum, and removal of volatile matter on arubber mill are common to all of these examples and should be understoodunless otherwise stated.)

Example II Another emulsion of chloro-2-butadiene-l,3 prepared by thesame method as Example I was allowed to polymerize for 18 hours at aboutroom temperature. This gave an 85.6 per cent yield of a polymer with aplasticity number of 7l75 which cured to give a product with a tensilestrength of 3125 pounds per square inch.

This cured material immersed in kerosene for 7 days at 100 C. showed anincrease of 62 per cent by volume. Example 111 per square inch wasobtained.

Example IV Two hundred fifty parts of chloro-2-butadiene- 1,3 wereemulsified in a solution containing 125 parts of 2 per cent cetyltrimethyl ammonium bromide aqueous solution and 625 parts of water.After emulsification, 250 parts of 1 per cent cetyl trimethyl ammoniumbromide aqueous solution containing '10 parts of sulphur dioxide wereadded. The sample was allowed to polymerize over night at about roomtemperature and gave a 67 per cent yield of a polymer with a plasticitynumber of 97 which cured to give a product with a tensile strength of2700 pounds per square inch.

Although, in each of the above examples, 4 per cent of sulphur dioxide,based on the weight of the chIoro-Z-butadiene-IB is employed, it hasbeen found that the amount of sulphur dioxide.

can be varied as illustrated in the following examples.

, Example V Two hundred fifty parts of chloro-Z-butadienee 1,3 wereemulsified in 916 parts of,2 per cent cetyl trimethyl ammonium bromideaqueous sotrimethylammonium bromide solution containing 8 parts ofsulphur dioxide. -'1he resulting emulsion was polymerized for 4 hoursjat20 C. and then coagulated and worked up in the usual manner. An 89percent yield was obtained of a product with a plasticity number of 83which cured to have a tensile strength of 3375 pounds per square inch.

Solvents or diluents may be used with the chloro-2-butadiene-1,3, as,for example, carbon tetrachloride,. toluene, benzene, and the like, asexemplified below. i

Example 1111 I Two hundred fifty parts of chlorb-Z-butadiene- 1,3 weredissolved in 250 parts of carbon tetra chloride and emulsified in 1000parts of 2 per cent cetyl trimethyl ammonium bromide aqueous solu tioncontaining 10 parts sulphur dioxide. After 16 hours at about roomtemperature, this gave 77.2 per cent yield of a product, withaplasticity number of 86,. which after compounding endear-- ing, had atensile strength of 2200 pounds per square inch.

Example IX Two hundred fifty parts of chloro-2-butadiene- I 1,3 werediluted with parts of carbon tetralution and 84 parts more of thesolution containing 4 parts of sulphur dioxide added. The

I emulsionv was cooled to 20 C. and allowed to polymerize over night atabout room temperature. This gave a 90 per cent yield of a product witha plasticity number of 130 which, after compounding and curing, had atensile strength oi 2875 pounds per square inch.

Example VI Two hundred fifty parts of chloro-2-butadiene-.

1,3 were emulsified in 708 parts of 2 per cent cetyl trimethyl ammoniumbromide aqueous solution and 292 parts more of the cetyl trimethylnumber of 128, which, after compounding and curing, had a tensflestrength of 2100 pounds per square inch. r

A high yield of plastic tially polymerized before it is emulsified andtreated with sulphur dioxide;

Example V11 One hundred ninety parts of chloro-2-butadime-1.3 wasallowed to stand at room temperature until it was 8.2 per centpolymerized. It was polymer is also obtained when thechloro-2-butadiene-L3 is par-,

then emulsified in 710 parts of aqueous 2 per centcetyl trimethylammonium bromide solution and treated with 88 parts of aqueous 2 percent cetyl chloride and emulsified in 250 parts of 2 per cent cetyltrimethyl ammonium bromide aqueous solution and 500 parts of water. Twohundred fifty parts of aqueous 2 per cent cetyl trimethylammoniurnbromide solution containing 10 parts sulphur dioxide were addedand the emulsion allowed to stand for 22 hours at about roomtemperature. A 75 per. cent yield of a product, with a plasticity numberof 87, which, after compounding and curing, had a tensilestrength of a3175 pounds per square inch was obtained.

Ashereinafter more fully set forth. this invention is not intended to belimited to the use of cetyl trimethyl ammonium bromide as theemulsifying agent in conjunction with sulphur dioxide.

.Many other emulsifying agents can be used as is illustrated by thefollowing examples.

" Example X One hundred parts of chloro-2-butadiene-1,3 were emusifiedin 360 parts of asolution containing 8 parts of octa decyl trimethylammonium bromide. Forty parts of water containing 4 parts of sulphurdioxide-were added and the emulsion allowed to polymerize for 20 hoursat about room temperature. This gave a 24 per cent yield of a polymerwith a plasticity number of 118 which.-

. after compounding and curing had a maximum tensile strength of 3925pounds per square inch.

Example XI One hundred parts of chioro-2-butadiene-L3- were emulsifiedin 360 parts of a solution containing 4 parts octa decyl trimethylammonium bromide, and 40 parts of water containing 4 parts of sulphurdioxide were added. After polymerization at about room temperature overnight, this gave an 84 percent yield of product with a plasticity numberof-86 which, aftercompoundlng and curing, had a maximum tensile strengthof 3850 pounds per square inch.

Example XII One hundred parts of chloro-2-butadiene L3- were emulsifiedin 360 parts of a solution contalngave a 92 per cent yield of productwith a plasticity number of 111 which, after compounding and curing, hada maximum tensile of 3575 pounds per square inch.

Example XIII Five hundred parts of chloro-2-butadiene-1,3 were dilutedwith 500 parts of benzene and emulsified with 2000 parts of 2 per centaqueous solution of the sodium salt of isopropyl naphthalenesulphonicacid and sulphur dioxide was passed in After 18 hours at aboutroom for 30 minutes. temperature thisgave an 82 per cent yield of aproduct which was definitely plastic, and, after compounding and curinhad a tensile strength of 1650 pounds per square inch.

' Example XIV 'Onehundred parts of chloro-2-butadiene-1,3

Example XV One hundred parts of chloro-Z-butadiene-LB were emulsified in360 parts of a 1.5 per cent aqueous solution of abietene sodiumsulphonate. Forty parts of water containing 2 parts of cetyl trimethylammonium bromide and 4 parts sulphur dioxide were added and the emulsionallowed to polymerize at about room temperature over night. An 84 percent yield was-obtained of a product which, after milling, had a.plasticity number of 66, and, after compounding and ouring, had amaximum tensile strength of 2975 pounds per square inch.

Example XVI One hundred parts of chloro-2-butadiene-L3 were emulsifiedin 360 parts of a 1 per cent aqueous solution of stearyl sodiumsulphate, and 40 parts of water containing 2 parts cetyl trimethylammonium bromide and 4 parts sulphur dioxide were added. Afterpolymerization at about room temperature, this gave an 82 per cent yieldof a product which, after milling, had a plasticity number of 136.

Similar results can be obtained if distenyl dimethyl ammonium bromide isused in place of cetyl trimethyl ammonium bromide in the above example.

i Example XVII Two hundred fifty parts chloroprene was emulsified andpolymerized as in Example I except that a 1 per cent'aqueous solution ofthe sodium thalene sulphonic acids.

v 2,871,719 tlon at about room temperature over night, this and washedwith warm water onamill with corrugated rolls for 45 minutes, thenmilled to constant weight on a mill with smooth rolls. A 98 per centyield of polymer with a plasticity num ber of 106 was obtained.

Example XVIII Fifteen parts of liquid sulphur dioxide were dissolved in100 parts of chloroprene at a temperature below C. and the solution wasimmediately emulsified by repeated passage through a centrifugal pump in212 parts of water containing 3 parts of sodium Lorol sulphate (seeExample XX) and 1 part of the sodium salts of the acids obtainedaccording to U. S. Patent No. 1,191,480 by condensing formaldehyde withnaphsion was kept at 40 C. until the density reached 1.080 which usuallyrequired about 50 minutes. The resultinglatex was then treated withamixture of 1 part of phenyl-beta-naphthylamine salts of sulphated cetyland stearyl alcohols was (dissolved in 1 part of benzene) and 1 part oftetra methyl thiuram disulphide dispersed in 3 parts of the emulsifyingsolution and with 1 part of dibutyl amine dissolved in ethyl alcohol.The

latex was then coagulated by the addition of a saturated sodium chloridesolution. The coagulum was washed with warm water and dried by millingon a rubber mill at about 50 C. Any unreacted sulphur dioxide wasvolatilized during these latter steps. A polymer, made in this way, whencompounded with 20 per cent of litharge and per cent of a soft carbonblack under the trade name of Thermax" and cured for 40 minutes at 153C., showed an absorption of only 17 per cent, by volume, when immersedin kerosene for 2 days at 100i C.

Example XIX A product was prepared exactly as in Example XVIII exceptthat 25 parts of sulphur dioxide, 2 parts of normal butyl alcohol(dissolved in the chloroprene) and 2 parts of the sodium .Lorol"sulphate, were used. The kerosene absorption was 11 per cent. I

The polymerization of chloroprene in the presence of sulphur dioxide maybe further modified by the method described in copending application ofStarkweather and Collins Serial No. 156,518, filed July 30, 1937 (forexample, by having a mercaptan present during the polymerization) or bythe method given in eopending application of Collins, serial No.204,305, filed April 26, 1938, consisting in having free sulphur presentduring the polymerization. The resulting prodnot is then plasticized,for example, with a thiuram disulphide and an amine as described incopending application of Youker, Serial No. 264,581, filed March 28,1939. The efiect of these modifications of the present invention is toincrease the plasticity of the polymer without, in general, decreasing.its resistance to swelling when cured. Thus, a preferred embodiment ofthe present invention includes the step of polymerizing in the presenceof both sulphur and sulphur dioxide. The following is an example of thisprocedure.

Example XX One hundred parts of-chloroprene, in which 15 parts ofsulphur dioxide, 0.24 part of sulphur, and 2 parts of oyclohexanol hadbeen dissolved, were dispersed at 10 C. in 212 parts of water con'taining 2 parts of sodium Lorol" sulphate (LoroP is a mixture ofstraight-chain, aliphatic The resulting disper alcohols with an averagechain length of about such as cetyl pyridinium bromide may also be 13carbon atoms made from cocoanut oil), and 2 parts of an emulsifyingagent of sodium salts of,-

the acids obtained by condensing naphthalene sulphonic acids withformaldehyde according to U. S. Patent No. 1,191,480, and polymerized at42 C. until the density was approximately 1.084 A dispersion of 1 partof the liquid .mixture of diphenylamine and phenyl-alpha-naphthylaminedispersed in aqueous sodium abietate solution, a

I dispersion of 1 part of tetramethyl-thiuram disulfide in the mixtureof emulsifying agents used above and a solution of 1 part ofdibutylamine in ethyl alcohol were then added to the latex which wasthen coagulated with salt. The polymer was washed with water on acorrugated mill and then dried by milling on a rubber mill in thepresence of 1 part of phenyl-beta-naphthylamine and 1 part oftetramethyl-thiuram-disulphide. The

plasticity number of the product was 94. Similar results were obtainedby using 2 parts of diorthotolyl guanidine in the place of 1 part ofdibutylamine.

used successfully. The chlorides or other soluble salts corresponding tothese bromides may also be used or compounds such as cetyl or octadecyclbetaines of the general formula cm om; c

in which R is a long chain aliphatic group, may be substituted as theemulsifying agents. The tertiary ammonium salts with long chain radicalsare less effective than the quaternary as emulsifying agents. 'Octadecyldimethyl ammonium bromide (stearyi dimethyl amine hydrobromide) anddiethylamino ethyl oleyl amide hydrochloride are examples of members ofthis class whlch have been used.

Other types of empulsifying agents which may be used are the solublesalts of (A) the sulphate -When compounded and cured as in the preceding examples, the kerosene absorption was 13 per cent.

The chloroprene used in the examples was substantially free fromacetaldehyde,' monovinylacetylene, divinylacety1ene, methyl vinyl ketoneand dichloro-1,3-butene-2. It is possible to obtain satisfactory,although somewhat inferior, results by the use of a less purechloroprene, particularly if the polymerization is interrupted when theyield is less than with the purer material. Thus, for example,chloroprene containing 0.3 percent acetaldehyde, 0.3 per centmonovinylacetylene, 0.1 per cent divinylacetylene and 0.3 per centmethyl vinyl'ketone may be used. In fact, it is sometimes observed thatsmall amounts of acetaldehyde and monovinylacetylene cause an increasein the tensile strength of the final product. It will be understood,therefore, that this invention is not limited to the use of pure chloro-2-butadiene-l,3 or other halogen-2-butadiene- 1,3, although the use of asubstantially pure halogen- 2-butadiene-1,3 is preferred. Accordingly,the impurities mentioned above or other corresponding ones should not bepresent in substantial amounts, if the most desirable results are to beobtained. The halogenbutadienes may be polymerized in the presence ofother materials, however, to produce useful products as is describedherein.

As is apparent from the above examples, this invention is not limited tothe use of any particular emulsifying agent in conjunction with thesulphur dioxide when the polymerization is to be carried out in theemulsion form. Several different types of empulsifying agents have beendisclosed above and applied to this invention, and,

closed in the Dales and- Downing Patent No.

2,138,226, above referred to, would be suitable, although, of course,all would not give equally desirable results. Cetyl and octa decyltrimethyl ammonium bromides illustrate a sub-class consisting of solublesaltsof quaternary ammonium bases which contain at least one long chainaliphatic group. Cyclic quaternary ammonium salts tinuously or in one ormore batches. Also, it is esters of long chain aliphatic alcohols (suchas the sodium salt of cetyl or octadecyl sulphate), of (B) sulphonatedunsaturated hydrocarbons (such as the sodium salt of abietene sulfonicacid), and of (C) naphthalene sulphonic acids containing hydrocarbonside-chains, such as the products obtained by condensing naphthalenesulfonic acids with formaldehyde.

Another type of emulsifying agent is illustrated by (D) the reactionproducts of a long chain primary amine with two'molecules ofepichlorhydrine or glycide. The use of an agent of type A is illustratedby Examples XVI and XVII, type B by Example XV, type C in Example XIIIand type D by Example XIV. Dispersions of the chlo roprene polymer insolutions of agents of types A, B, and C may be coagulated by theaddition of sodium chloride or other water-soluble salt.

Dispersion containing agents of typeD may be coagulated merely by makingalkaline to Brilliant Yellow and heating to 60 C. The 'coagula are thenwashed with water to removethe salt and dispersing agent, which, ifallowed to remain, would increase the difhculty of milling and also tendto decrease the quality of the cured polymer.

The amount of such emulsifying agents to be employed will, of course,depend upon the effectiveness of the particular agents. Amounts ofemulsifying agent ranging from 2 per cent up to 8.4 per cent, based onthe chloro-butadiene, are employed in the specific emulsions describedabove. -Greater or less amounts of these or other similar agents may beused. The amount necessary is readily determined by experimental trialin any given case. At least an amount sufficient to prevent separationof a solid or liquid phase, should be present, but if desired, more canbe used. It has been observed, as illustrated in Examples 11, I11, andIV, that increasing the amount of emulsifying agent, in general, resultsin increasing the speed of polymerization. The present inventionincludes, within its scope, the use of all concentrations and amounts ofemulsifying agents which give stable empulsions (i. e., emulsions inwhich a solid or liquid phase does not separate out) of halogenbutadienein the presence of sulphur dioxide. It is also possible to add moreemulsifying agent during the course of the polymerization, if desired,either conoften desirable to increase the acidity of the emulsion,containing for example, sulphur dioxide, by addition of acid, such ashydrochloric, for example, in such a quantity that the emulsion willturn Congo redpaper to a decided blue color.

Sulphur dioxide may be added to the emulsion in any convenient manner,such as, by the direct addition of the gaseous sulphur dioxide or by theaddition of a'solution of'sulphur dioxide in water or in the emulsifyingsolution or inchloromoting an improved yield of a more plastic polymerfrom the chloroprene. Where this improvement in plasticity is the onlyeffect sought, ranges of added sulphur dioxide from 1.6 per cent to 5.6per cent, based on the chloroprene, are quite satisfactory. althoughthese percentages do not mark the limits of the invention.

'. It will be noted that, in a number of the above examples, chloropreneis dispersed in the emulcentrations of halogen butadiene, in emulsionsparticularly, for various reasons, but it is, nevertheless, to beunderstood that the invention is not limited to the particularconcentrations of chlorosifying solution in about per centconcentration, and that it is then polymerized in the presence of about4 per cent of sulphur dioxide based on the .chloroprene. Such examples,therefore, illustrate embodiments involving the preferred conditionswhere only high yieldof very plastic polymer is important, whichcomprise the use of about 4 per cent of sulphur dioxide based on thechloroprene, and the use of emulsions in which the concentration of thechloroprene may vary from 20 to 30. per cent.

Where it is desired to produce a polymer which,

I when cured, has an improved solvent resistance,

it is desirable to increase the amount oi sulphur dioxide. Although evena small proportion of the sulphur dioxide has a definite effect upon thesol-- vent resistance of the polymer, it is preferred to have at least 5per cent in chemical combination where the increase in the solventresistance is an important consideration.

In general, all of the sulphur dioxide added does not 'enter into stablecombination with the chloroprene. When very large proportions of sulphurdioxide, for example equimolecular amounts of chloroprene and sulphurdioxide, are

- used, the amount of sulphur dioxide in stable combination does notexceed about per cent of the product. As the sulphur dioxide contentincreases, the solvent resistance increases, but the rubbery propertiessuch as resiliency, elongation, and tensile strength of the curedpolymer as well as the plasticity in the uncured state tend to deprene,employed in the above examples,

The sulphur dioxide need not all be added at one time. Thus, the processin Example II may be altered by adding only 5 parts of sulphur dioxideirnmediately after emulsification and the remaining 5 parts alter thepolymerization has proceeded for 1 hour. A yield of 93 percent ofpolymer with a plasticity number of was obtained. Further variationsconsist, for example,

in adding the second portion after two hours, or

partly after one and partly after two hours or continuously during thefirst one or two hours of the polymerization. The sulphur dioxide may beadded before, during, or after the emulsification step. It has beenobserved that the formation of insoluble, granular polymer, whichsometimes causes trouble in some polymerization processes, does not takeplace when chloro-2-butadime-1,3 is polymerized in emulsion in thepresence of sulphur dioxide. The same is true of the formation of thevolatile, odorouspolymers.

The improved process described herein is, moreover, applicable not onlyto emulsions in water, but also to the polymerization of halogen- 2-butadiene-l,3, emulsified in other suitable liquids, in which thehalogen-2-butadiene-1,3 can be'emulsified and which do not prevent thepolymerization of the halogen butadiene and which preferably does noteven inhibit its polymerization, such as glycerol, glyccls andformamide. Emulsions of this type are broadly disclosed in the U. S.Patents to Carothers, No.

2,080,558, issued May 18, 1937, and to Dales and sifying liquid througha gear pump or a cencrease. Consequently, it is preferred to poly'mer- Iize in the presence of such a percentage of sul- I phur dioxide as willgive from 5 to 15 per cent of combined sulphur dioxide in the product;that is, to polymerize in the presence of from 5.6 to about 30 per centof sulphur dioxide, based on the chloroprene, where resistance tosolvents is important.

It is understood, of course, that sulphur dioxide is a gas at ordinarytemperatures, and unreacted volatile sulphur dioxide is removed in theworking of the polymer. (See Examples I and XVIII.)

In emulsion polymerization, and also in solution polymerization, it ispossible to further vary the manner of applying the invention by varyingthe concentration of the halogen butadiene in the emulsion or solution,as the case may be. There trifugal pump or by turbulent flow or byagitating the materials with a paddle or stirrer or by shaking them in asuitable container.

While about 20C. tc 60 .C-., is the preferred polymerization temperaturerange, it has been found that the polymerization may be effected attemperatures ranging from 0 to C. Therate of polymerization is favorablyaffected by in creasing the temperature so that the time ofpolymerization required to produce similar products will change somewhatwith changes in temperature. The rate of polymerization is alsofavorably affected by increasing the pressure and also by increasing theconcentration of the emulsifying agent, as illustrated by Examples II,III, and IV.

The products produced by the processes illustrated in the above exampleswill naturally vary considerably in their characteristics, dependingupon the particular conditions employed. The

'extent of polymerization (proportion of chloro- 2-butadiene-l,3consumed) has been found to have a considerable efiect'upon theproperties of the polymer, particularly its plasticity number, as shownabove in Examples I and II and in XI and XII. It has been found that theplasticity number may be accurately controlled by detercussed above, maybe added at any time after mining the extent of polymerization from timeto time and interrupting the polymerization (for example, by addingphenyl-beta-naphthylamine), when the proportion of chlorobutadienepolymerized has reached the value, determined by previous experiment,corresponding to the desired plasticity. In general, and particularlyunder preferred conditions, it has been found that very good results areobtained if the poly- 'merization is stopped sometime after '15 per centof polymer has been formed. The extent of the polymerization may bedetermined in a number of ways. The amount of polymer formed maybedetermined directly, for example, by coagulating and drying a sample ofthe latex, or, conversely, the extent of the polymerization may bedetermined by measuring the amount of unchanged chlorodiene recovered byany known emcient method (for example, distillation) from the latex orfrom the serum obtained by coagulation with alcohol. The density of thelatex, which is approximately a linear function of the extent ofpolymerization, may also be used to follow the reaction. An experiencedoperator can also roughly estimate the extent of polymerization from theconsistency of a coagulated sample. In certain cases, it, may bedesirable to recover the unchanged chlorobutadiene for reuse. This maylar agents may be used in place of phenyl-beta-' naphthylamine. Itis,-preierably, added in the form of an aqueous emulsion. Frequently itis dissolved in benzene or other suitable solvents beforeemulsification. The method disclosed in chanically generated heat in thelatter case asing to a constant weight. This phase of the the examplesproduces very good results, but it will be understood that it may beadded in any other convenient way, if desired. It may also be now U. S.Patent 2,259,122, the tendency of the product of the presentinvention todecrease in plasticity on prolonged storage is also greatly reduced byincorporating a compound of the general formula which group, it will benoted, is characterized by havinga central carbon, one of the valencesof which is satisfied by a sulphur atom and the other three valences ofwhich are satisfied by a nitrogen atom and another sulphur atomtogether, such, for example, as tetramethyl thiuram disulfide. Theseagents, which are preferably used together with the antioxidants disthepolymerization has been completed.

The polymer may be. isolated from the aqueous emulsion by any suitablemethod, for example, by adding ethyl alcohol, as shown in Example I.

The polymer may also be obtained from the latex by spray drying or byevaporation of thin films. Coagulation may alsobe carried out asdisclosed in U. S. Patent 2,161,949, and U. 8. Patent 2,187,146.

Unless the emulsifying agent is completely removed from the polymer inthe coagulation step, it may be desirable. to remove substantially allof it before the final milling. This is conveniently accomplished bywashing with warm water on corrugated rolls or in an internal mixer, bywhich methods new surfaces of the polymer are being continuously exposedto washing medium. To assist the extraction of the emulsifying agent,

alcohol, acetone, or similar solvent which dis-.

solves emulsifying agent, but not the polymer, may be used.

The coagulum, after being washed, if necessary, may be dried, forexample, in a current of air at elevated temperatures up to about C.

or at sub-atmospheric pressure or by washing with alcohol, or may bemilled directly, the mesisting the removal of the water. The temperatureof the polymer being milled, however, preferably will not exceed about100 C. and is pref The rolls of the mill should,

erably much less. therefore, be cooled, for example, with cold water orrefrigerating brine.

Volatile material can be removed to any desired extent, by any suitablemethod, for example, by working the coagulated polymer on a rubber mill,substantially all of it being removed by workprocess may be practiced inother ways, however. As appears from the examples, it is possible tocomplete the polymerization in emulsion after partial polymerization inthe massive form. The specific illustration in Example VII describes anexperiment where chloroprene was emulsified when it was 8.2 per centpolymerized but it will be understood that the halogenbutadiene may beused in the process of the present invention not only when it containsless amounts of polymer,

but also when it contains greater amounts. Care must be taken, however,not toallow the polymerization in the massive state to proceed to apoint where substantial amounts of the elastic polymer are formed, ifmaximum yields of plastic polymer are desired.

The further polymerization in emulsion of the partially polymerizedhalogenbutadiene may be modified in the various particulars describedabove for the monomer. The sulphur dioxide may be added either before orafter emulsifica tion or even before partial polymerization.

It has been stated above that it is generally desirable to removesubstantially all of the emulsifying agent before final milling. Thisstatement is subject to exception where an ammonium salt is used as theemulsifying agent. It has been found that the ammonium salts are capableof exerting a stabilizing effect on the plastic polymers. They tend toprevent them from losing their plasticity. It is, therefore, gen erallydesirable to avoid removing these salts from the polymer, insofar aspossible during the coaguapplication, is meant any ammonium salt,either.

iienes-1,3,

'resulted.

naphthylamine in the usual manner followed by substituted orunsubstituted, unless the term is )therwise qualified.

It has also been found that halogen-2-butaspecificallychloro-2-butadiene-L3, may be polymerized in the presence of othermaterials, such as film-forming materials, for example, polymerizablematerials containing two :arbon atoms in an open-chain joined by morethan one bond, by the methods described above,

to produce similar results. A preferred embodiment involves the use ofpolymerizable materials ofthe class described, which are miscible withchloroprene. The polymerization of the halogen-2-butaclienes in thepresence of such materials is illustrated by the following examples,

which describe the polymerization of chloroprene in emulsion as thepreferred embodiment.

Example XXI A mixture of 90 parts of chloro-2-butadiene- 1,3 and partsof methyl acrylic nitrile were emulsified in 400 parts of aqueous 2 percent cetyl trimethyl ammonium bromide containing 4 parts of sulphurdioxide. After 4 hours at about room temperature, this gave 90 parts ofa product with a plasticity number of 100, which, after compounding andcuring, had a tensile strength of 2425 pounds per square inch.

Example XXII A mixture of 180 parts of chloro-2-butadiene- 1,3 and partsof methyl methacrylate were emulsified in 800 parts of aqueous 2 percent cetyl trimethyl ammonium bromide containing 8 parts of sulphurdioxide. After o hours at about room temperature, this gave 170 parts ofa product withaplasticity number oi" 100 which, after compounding andcuring, had sile strength of 3000 pounds per square inch;

Example XXIII A mixture of 160 parts of chioro-2-butadiene- 1,3 and 40parts of methyl methacrylate was emulsified in 800 parts of aqueous 2per cent cetyl trimethyl ammonium bromide containing 8 parts sulphurdioxide. After 4V hours at about room temperature, this gave 152 partsof polymer with a plasticity number of 95, which, after compounding andcuring, had 'a tensile strength of 2325 pounds per square inch.

Example XXIV Twenty parts of butadiene were dissolved in 180 parts ofchloro-2-butadiene-l,3 and the solution emulsified'in 800 parts aqueous2 per cent cetyl trimethyl ammonium bromide containing 8 parts sulphurdioxide. After 4%; hours at about room temperature, this gave an 85 percent yield of polymer with a plasticity number of 121, which,

9 after'compo'unding and curing, had a tensile strength of 2825 poundsper squareinch.

Example XXV Thirty-one part of butadiene (92 per cent pure), 20 partsofchluro-2-butadiene-L3, 2.4 parts of sulphur doxide, and 70 part of a 2per cent solution of cetyl trimethyl ammonium bromide were sealed in athick-walled glass tube containing air and agitated at 60" C. for 112hours. A thick latex containing some coagulum Addition of 0.5 part ofphenyl-beta coagulation by the addition of ethyl alcohol and sodiumchloride and milling to constant weight gave 9.139 per cent yield ofmixed polymer containing 21.5 per cent chlorine corresponding to 53.8per cent of cli1oro-2-butadiene-1,3. The polymer had a plasticitynumberof 287 and, on curing for minutes at 141 C., in a mixture composed of100 parts, by weight, of the polymer, 50 parts of carbon black, 2 partsof stearic acid, 5 parts of zinc oxide, 2. parts of sulphur, and 1.25parts of mercapto-benzothiazol, gave a tensile strength of 1675 pounds.If the polymerization was carried out in the same manner, except that nosulphur dioxide was used, the yield was substantially the same percent),'but the plasticity number wa 470 and the tens 1e strengthobtained.

only 425 pounds;

The polymerization of halogen-2-butadiener- 1,3 and particularly ofchloro-2-butadiene-l,3 in the presence of other materials is broadlydisclosed in U. S. patents to Carothers, Collins and Kirby, No.2,029,410, issued February 4, 1936, and Nos. 2,066,329, 2,066,330, and2,066,331,,ali issued January 5, 1937., In general, the process of thepresent invention is applicable to the polymerizations described inthose patents as is apparent from the above illustrative examples.

' It has been stated that this invention is appli cable both broadly andspecifically to homologous 3-substituted halogen-2-butadenes-L3 as wellas to the halogen butadienes themselves. The polymerization of one ofthese homologues in the presence of sulphur dioxide is illustrated bythe following examples.

Example XXVI Example XX VII Two'yihundred and fifty parts of bromoprenewaspolymerized exactly like the chloroprene in Example IV of theapplication except that 15 parts of sulphur dioxide was used and thepolymerization was carried on for 50 minutes at 20.

C. Ninety-one per cent of a plastic product was Itis possible to carryout the process of the present invention continuously. Thus, thechloroprene may be continuously emulsified by introducing it togetherw.th an emulsifyingsolution into a suitable emulsifier a describedabove, said emulsifier being of such construction that the chloropreneis thoroughly emulsified during its passage therethrough. The modifyingand other agents can also be added with the chloroprene continuouspolymerization of chloroprene is also advantageous. Such continuouspolymerization may be readily effected by passing a stream comprisingthe chloroprene, for example, an emulsion' of chloroprene containingsulphur dioxide through a suitable vessel, for example, a tubemaintained at the-desired temperature by suitable means, such as a bath,at such a rate that the efiluent product from the polymerization ves-'sel has reached the desired stage of polymerization. Continuouspolymerization in the presence of a modifying agent is quiteconveniently effected when the chloroprene is in an emulsified state.

and starting with the chloroprene and other ingredients of theemulsiomthe plastic polymer may be produced continuously by continuouslyemulsifying as described above and then passing the stream of emulsionso prepared for polymerization into the polymerization vessel andtherethrough, as described.

If desired, an antioxidant, such as phenyl-betanaphthylamine, or astabilizer such as tetra methyl thiuram disulphide, may readily beincorporated continuouslyinto a stream comprising the polymer, forexample, the stream issuing'from the continuous polymerization vessel,by admitting into the stream comprising the polymer a stream comprisingthe antioxidant, the stream of antioxidant being admitted at such a ratethat the desired amount of antioxidant is added.

C. to 160 C., to strong, tough, highly elastic products resemblingnatural rubber in all essential points and having the additionaladvantage of being much more resistant to the action or organic solventsand chemical reagents generally and of not requiring the use of sulphurand organic accelerators.

Hence, it is obvious that their properties are much the same as theproperties of the polymers of chloroprenedescribed by Williams in his U.S.

Patent No.4 ,950,436. They may, therefore, be

put to the same uses as he mentions for his products as well as toothers not mentioned by him specifically, although included by his broaddescription, such as, for example, coating compositions when dissolvedin suitable solvents such .as benzene, etc.-, to act'as adhesives forwood, glass. metal, paper, cloth, leather, and the like, or they may beused for the impregnation of porous materials. These polymers may alsobe put to the uses described for the polymers of chloro-2-butadime-1,3produced by prior processes in the articles appearing in Ind. Eng. Chem.25, 1912 (1933),

of this invention have an additional point of novelty in that theycontain sulphur dioxide in chemical combination.

As shown in the examples, the productproduced by the process of thepresent invention may be compounded and/ or moulded and cured to agreatvariety of elastic products. A wide variety of compoundingingredients and compositions of chloro-2-butadiene-1,3 polymer have beendisclosed in the Duprene Manual," published August; 1, 1934, by E. I. duPont de'Nemours and Company as well as in U. S. Patent No. 1,950,436 andthe Ind. Eng. Chem. articles, cited above. The methods described thereinare applicable to polymers produced by the process of this invention.The nature of the compounding ingredients and the proportions in whichthey are used, of course, vary with the use to which the compounded polymer is to be put. In general, it may be said that the polymers'of thisinvention may be compounded, cured, and used in the manner described forthe plastic polymers of chloro-2-butaciiene-1,3 produced by previouslyknown methods.

Thus, while zinc oxide, magnesium oxide, and rosin have been used inmost of the examples given above, it is to be understood that carbonblack and other compounding ingredients used with previously knownplastic polymers of chloro- 2-butadiene-l,3 may also be used withthoseproduced by the process of the present invention. It is generallypossible also to add some or all of the compounding ingredients, in theform of dispersions in water, to the latex before coagulation. It willbe noted, however, that the methods of compounding and curing differ insome respects from those used for natural rubber.

Alternatively, the polymer dispersion or latex obtained as anintermediate in the course of carrying out the present invention may beused as such, with or without the addition of compounding ingredients,but preferably after the addition of antioxidants as described above. Inaddition, many compounding ingredients may be added to the dispersionprior to polymerization, if desired. The uses of the dispersion are,however, the same as those of natural rubber latex. Thus, for example,it may be used in the preparation of thinwalled articles such as glovesand toy balloons, by dipping a form of suitable shape into the latex,

withdrawing, coagulating, and drying the adher- 28, 33 (1934); and in"Rubber Age for December ing layer, and, if desired, repeating theprocess, as described by Kirby in U. S. Patent No. 2,076,949, issuedApril .13, 1937. The articles may then be made elastic by theapplication of heat. Similarly, latex may be advantageously used forimpregnating, coating, or otherwise treating porous or fibrous materialssuch as paper, cloth, felt, or leather, according, in part, to theteachings of Collins and Larson in U. S. Patent No. 1,967,863, followed,if desired, by curing by the application of heat.

The present invention, therefore, provides a obtained thereby presentnumerous improve-.

, ments over previous inventions in this field.

1 It is apparent that manywidely different embodiments of this inventionmay be made without departing from the spirit and, scope thereof,

and, therefore, it is not intended to be limited except as indicated inthe appended claims.

I claim:

1. The process of making rubber-like materials which comprisesemulsifying, in water, a compound of the general formula in which x ishalogen and R is a member of the group consisting of hydrogen andhydrocarbon radicals, and polymerizing the dispersed compound in thepresence of sulphur dioxide to produce a polymeric, rubber-like productcontaining not more than per cent of the combined sulphur dioxide basedon the weight of the product.

2. The process of making rubber-like materials which comprisespolymerizing in emulsion bromo-2-butadiene-1,3 in the presence of from90 cent of combined sulphur dioxide based on the weight of the product.

4. The process of making rubber-like materials 85 which comprisespolymerizing in emulsion chloro- 2-butadiene-l,3, in the presence ofanother polymerizable material containing two carbon atoms in an openchain Joined by more than one bond. and in the presence of from aboutl.6 per cent to about per cent of sulphur dioxide based on the weight ofthe total polymerlzable materials to produce a polymeric, rubber-likeproduct containing not more than 25 per cent of combined sulphur dioxidebased on the weight of the product.

compound of the general formula n-c=o-o=o-n like in which x is halogenand R is a member of the group consisting of hydrogen and hydrocarbonradicals, said polymer having sulphur dioxide in chemical combinationtherewith, the combined sulphur dioxide not exceeding 25 per cent basedon the weight of the derivative.

6. A heat curable, rubber-like polymer of chloro-2-butadiene-1,3 havingsulphur dioxide in chemical combination therewith, the combined sulphurdioxide not exceeding 25 'per cent basedon the weight of the polymer. Y

' '7. In the process of forming a rubber-like, polymeric derivative ofchloro-2-butadiene-L the step of polymerizing said chloro-z-butadiene-1,3 in emulsion in the presence of about 1.6 per cent to about 5.8 percent of sulphur dioxide based on the weight of the chloro-2-butadiene-5. A heat curable, rubber-like polymer of 9.-

ing of soluble salts of quaternary ammonium bases which contain at leastone long-chain aliphatic group, soluble salts of tertiary ammo-- niumbases which contain at least one longchain aliphatic group, solublesaltsof the sulphate esters of long-chain aliphatic alcohols, solublesalts of sulfonated unsaturated hydrocarbons, soluble salts of alkylnaphthalene sulphonic acids, the reaction products of a long-chain primmary amine with two molecules of epichlorhydrine and the reactionproducts of a long-chain primary amine with two molecules of glycide,and then polymerizing the emulsified chloro-Z-butadime-1,3 in thepresence of about 1.6 per cent to u about 5.6 per cent of sulphurdioxide based on the weight of chloro-2-butadiene-1,3.

9. In the process of forming a rubber-like, polymeric derivative ofchloro-2-butadiene-1,3, the steps which comprise emulsifying saidchloro- 2-butadiene-l,3, in water, in the presence of a soluble salt ofa quaternary ammonium base, containing at least one long-chain aliphaticgroup, and then polymerizing said dispersed chloro-2-butadiene-l,3 inthe presence of about a5 1.6 per cent to about 5.6 per cent of sulphurdioxide based on the weight of the chloro-2-butadime-1,3. I

10. In the process of forming a rubber-like, polymeric derivative ofchloro2-butadiene-l,3, the steps which comprise emulsifying saidchloro-2-butadiene-l,3, in water, in the presence of asoluble salt of aquaternary ammonium base,

containing at least one-long chain aliphatic group, and thenpolymerizing said dispersed chloro-2-butadiene-1,3, at a temperature ofabout 20 C., in the presence of about 4 per cent of sulphur dioxidebased on the weight of the chloro-2-butadiene-l ,3.

'11. In a process for continuously producing a so p lymeric, rubber-likederivative of chloro-2- butadiene-1,3, the steps which comprisecontinuously emulsifying chloro-2-butadiene-l,3, in water, continuouslyadding sulphur dioxide in an amount equal to about 1.6 per cent to about5.6 per cent, by weight, of the chloro-2-butadime-1,3 added,andcontinuously polymerizing the dispersed chloro-2-butadiene-l,3 in thepresence of the sulphur dioxide.

12. A heat curable, rubber-like polymer of 5 chloro-2-butadiene-1,3having in chemical combination with it about 3 per cent of sulphur.dioxide based on the weight of the polymer.

13. The process of forming a rubber-like, polymeric derivative ofchloro-2-butadiene-1,3, the

step of polymerizing chloro-2-butadiene-i,3 in

aqueous emulsion in the presence of about 5.6

per cent to about 30 per cent of sulphur dioxidebased on the weight ofthe chloro-Z-butadiene- 1,3.

14. In the process of forming a rubber-like, polymeric derivative ofchloro-2-butadlene-l,3, the steps which comprise emulsifying saidchloro-2-butadiene-l,3, in water, and then polymerizing said emulsifiedchloro-2-butadiene-1,3

in the presence of about 5.6 per cent to about 30 per cent of sulphurdioxide based on the weight of the chloro-2-butadiene-1,3..

15. In a process for continuously producing a polymeric, rubber-likederivative of chloro-Z- .3- butadiene-lfi, the steps which! comprisecon- 8.'In the proces f min a rubber-like. tinuously emulsifyingch1oro-2-butadiene-1,3, in P lymeric derivative of chloro-2-butadiene-.- water, continuously adding sulphur dioxide in an thesteps which com rise emulsifying; said amount equal to about 5.6 percent to about 30 chloro-2 -butadiene-1,3, in water, in the presence ofan emulsifying Heat of the groupconsist- 751.3 added, and continuouslypolymerizing the per cent, by weight. of thechloro-2-brutadienedispersed chIoro-2-butadiene-I,3 in the presence ofthe sulphur dioxide.

16. A heat curable, rubber-like polymer of chioro-2-butadiene-1;3 havingin chemical combination therewith sulphur dioxide in an amount 6 ofabout 5 per cent to 15 per cent of sulphur dioxide based on the weightof the polymer.

17. The process of making a rubber-like material which comprisesemulsifying, in water, a compound of the general formula H-C=CC=CH inwhich X is halogen and R is a member of the group consisting of hydrogenand hydrocarbon radicals and polymerizing thedisper'sed.

compound in the presence of from 1.6 per cent to 30 per cent sulphurdioxide based on the weight of the said compound of the general formula.

HOWARD WARNER BTARKWEATHER.

